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Jan Rajchman, the Selectron

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Jan Rajchman, the Selectron THE ANNALS OF'THE COMPUTATION LABORATORY OF HARVARD UNIVERSITY VOLUME XXVI PROCEEDINGS OF A SECOND SYMPOSIUM ON LARGE-SCALE DIGITAL CALCULATING MACHINERY Jointly Sponsored by The Navy Department Bureau of Ordnance and Harvard University at The Computation Laboratory 13-16 September 1949 CAMBRIDGE, MASSACHUSETTS HARVARD UNIVERSITY PRESS ~95I LONDON : GEOFFREY CUMBERLEGE OXFORD UNIVERSITY PRESS The opinions or assertions contained herein are the private ones of the writers and are not to be, construed as official or reflecting the views of the Navy Department or the naval service at large. Composition by The Pitman Press, Bath, England Printed by offset lithography by the Murray Printing Company, Wakefield, Massachusetts, U.S.A. PREFACE InJanuary 1947 the Bureau of Ordnance of the United States Navy and Harvard Univer­ sity together sponsored a Symposium on Large-Scale Digital Calculating Machinery as a means of furthering interest in the design, construction, application, and operation ofcomputing machinery. This meeting was attended by over three hundred people, nearly four times the originally expected attendance, and by popular aemand the proceedings were published as Volume XVI of the Annals of the Computation Laboratory. At the Oak Ridge meeting on computing machinery in April 1949, Mina Rees and John Mauchly, representing the Association for Computing Machinery, suggested that another symposium should be held at Harvard summa~izing. recent and current developments. The staff of the Computation Laboratory had already considered this possibility in connection with the announcement of the completion of Mark III Calculator, and were delighted with the suggestions of Dr. Rees and Dr. Mauchly. Accordingly, the Bureau of Ordnance was again invited to join Harvard University in sponsoring a second symposium with emphasis on the application of digital calculating machinery. From experience with the first symposium, it was expected that. perhaps three hundred people might attend. The response of more than seven hundred participants clearly indicated the rapidity with which the field of automatic computation is growing. T~is volume, the twenty-sixth of the Annals of the Computation Laboratory, contains all the papers presented at the second symposium except one. Two of the speakers, Manuel S. Vallarta and Frederick V. Waugh, found at the last minute that they were unable to attend. However, their papers were received and were read by J. Curry Street and Leon Moses, respectively, both of Harvard University. Because of the tremendous editorial difficulties experienced with the proceedings of the first symposium, each speaker at the second was requested to supply his manuscript in advance, in order to avoid dependence upon transcription from sound recording. Thirty-nine papers are herein published essentially as submitted. Thus the work required to prepare this volume for publication was greatly reduced. However, it was necessary to redraw many of the illustrations for offset reproduction; this was done by Carmela M. Ciampa, assisted by Paul Donaldson, photographer of Cruft Laboratory, Harvard University. Since the symposium was held iIi September, prior to the opening of the fall term, it was possible to make use of the dormitories in the Harvard Yard and the dining facilities of the Harvard Union. Arthur Trottenberg of Harvard University supervised arrangements for the use of these facilities and other accommodations. Preparation of the program and regis­ tration lists and the registration of the members of the symposium after their arrival were carried out by Betty Jennings, Jacquelin Sanborn, Jean Crawford, and Holly Wilkins. It is v PREFACE a pleasure to acknowledge the cooperation of Edmund C. Berkeley, secretary of the Association for Computing Machinery, in this connection. The staff of the Computation Laboratory wishes to express its appreciation to the members of the symposium for their attendance and for their participation in the discussions, to the chairmen of the several sessions for their assistance, and to the speakers not only for their addresses during the symposium but also for their cooperation in preparing the manuscripts of their papers. The staff also wishes to express its gratitude to the Bureau of Ordnance and to its repre­ sentatives, Captain G. T~ Atkins and Mr. Albert Wertheimer, for many years of pleasant association throughout the building of Mark II and Mark III Calculators, for their continued i~terest and help, and for making possible both the Second Symposium on Large-Scale Digital Calculating Machinery arid the publication of its proceedings. HOWARD H. AIKEN Cambridge, Massachusetts May 1950 VI THE SELECTRON JAN RAJCHMAN Radio Cor/Joration of America The initial work on a special type of electrostatic memory tube, called the Selectron, was reported on January 8, 1947, at the first Symposium on Large-Scale Computing Machinery.! The present paper is a report of the tube developed as a result of work in progress since that date. Important changes in the initial tube were found necessary to obtain a practical and reliable device for use in electronic computers. The memory of an: electronic computer can be idealized as a large set of cells, each iden­ tified by a coded address and each capable of retaining a single on-off signal. A combination of such signals occurring simultaneously on several channels or sequentially on a single channel constitutes a number. The memory will be particularly useful if the occurrence of the set of pulses specifying the address will give access to the signal stored, or to 1;>e stored, in the shortest possible time without consideration of any previous selection. A device with such a digitalized address system and such direct access to any stored signa~ can be used singly or in groups in a most flexible manner, since no amplitude-sensitive qualities have to be dealt with and no specific sequences are intrinsic to the memory. The Selectron (Fig. 1) is a vacuum tube designed in an attempt to realize such an ideal memory device. The principle of the tube depends on quantizing both the address of the stored information and the information itself. The selection of the address is obtained by means of two orthogonal sets of parallel spaced metallic bars forming a checkerboard of win­ dows. A shower of electrons impinges on this checkerboard. Electrons are stopped in all windows except in a selected one by applying address-selecting voltages to certain groups of bars connected into appropriate combinations. The storage is in terms of the two stable potentials that tiny floating metallic elements, located in register with the windows, assume under continuous electron bombardment. The reading signals .are sizable electron currents passing through a hole in the storing elements. The signals produce also a visual monitoring display. The basic principle of the Selectron has not been changed. The main improvement is the use of discrete metallic eyelets as the storing elements. In addition to very reliable storage, . these eyelets have a "grid-action" effect yielding strong electronic reading signals. , The Selectron tube, called SE256, has 256 storing elements, is 3 in. in dIameter arid 7 in. long, and utilizes a 40-lead stem. The diametral and axial cross sections of the tube are shown in Figs. 2 and 3. Eight elongated cathodes of rectangular cross section are located in a diametral plane of the tube. Between and parallel to the cathodes are a set of nine selecting bars of square cross section. These vertical selecting bars are connected into six groups: VI' V2, V3, V4, JAN RAJCHMAN and Vl', V2', as shown in Fig. 4. On either side of the plane of the cathodes and V bars there is a set of 18 parallel bars of square cross section at right angles to the V set. These two sets of horizontal selecting bars sandwich the cathodes and V bars as do all subsequent electrodes FIG. 1. The Selectron. of the tube, the tube being symmetrical with respect to the cathode plane. The 36 horizontal selecting bars are connected in 12 groups: Hl to H4 and Hl' to Hs', as shown in Fig. 4. There are nine vertical bars for eight gates and 36 horizontal bars for 32 gates, the excess bars taking care of the end effects. On either side beyond the horizontal bars there is a collector made of two flat plates perforated with round holes whose centers match the centers of the windows formed by the 366 THE SELECTRON V and H-bars. Adjacent to the collector plates there are two perforated mica sheets holding between them 128 metallic eyelets. These eyelets, made on automatic screw machines, have a conical head, a center hole, a holding collar and a shielding tail. They are nickel-plated . FIG. 2. Diametral view of Selectron. steel. On the other side of the two mica plates is another perforated metal plate-the writing plate. The two collector plates, the two eyele~ mica plates, and the writing plate form a tight assembly riveted together at the ends and in the center. Beyond the writing plate is another metal plate-the reading plate-perforated. with holes in register with the holes of the other plates. Beyond it is a Faraday cage fonned by two perforated plates spaced some distance apart and closed on all four sides by a metallic wall. 367 FIG. 3. Axial cross section of Selectron. 368 THE SELECTRON A glass plate coated with a fluorescent material is placed against the outer plate of the cage. In the central plane of the cage there are nine wires which are spaced so as to be between the holes of the perforated plates. These reading wires are connected together and the corresponding lead to the stem is shielded. In the quiescent state of the tube storing informa- ~,:.. ---++----,.----t-----r--- lion previously written-in, all the selecting bars are m [6 1Tl, [E i3, ~ i4 ' ,0, ~ at the potential of the cathodes (0 v) and all other 4'; I ± = = I electrodes at potentials indicated in Fig.
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